指出这三个句子在一般情况下应该用什么语调。
①—Shall we go to the shopping centre by bike or by bus？

②—By bus.

③—How far is it from here？

A、①升调②降调③降调

B、①降调②降调③降调

C、①升调②降调③升调

D、①降调②降调③升调